Existing methods for controlling activation of a vehicle occupant restraint system work according to the following: the intensity with which a vehicle is delayed is continuously detected so that a function of the acceleration with time materializes. This function is continuously derived parallel to measuring the delay so that, expressed on the basis of an evolution of an acceleration curve over the time, the gradient of the acceleration curve can be established. This gradient is compared to a predetermined gradient threshold value. As soon as this gradient threshold value is attained the vehicle occupant restraint system is activated.
The aforementioned method used hitherto for controlling activation of a vehicle occupant restraint system has the drawback that it may take too long in some circumstances until a second stage of a multistage gas generator is activated since activation does not occur until a gradient threshold value is attained. Since differing parts of the vehicle, deformed one after the other, may also absorb differing work of deformation, the acceleration values may fluctuate very strongly. This is why, as a rule, the gradient of the acceleration is averaged. Since the averaged acceleration as described before increases only relatively slowly, circumstances may arise in which the gradient threshold is attained relatively late which may result in delays in activating the restraint system.
From DE 29 44 319 A1 a multichamber gas bag is known which depending on the strength of delay in an accident is inflated partly or completely by several ignition stages activatable one after the other. For this purpose a sensor system for sensing the delay is provided which activates the first or, displaced herefrom in time, also further ignition stages of a gas generator. How this sensor system works precisely, however, is not stated in this document.